The invention relates generally to broadband wireless access communications networks. More specifically, embodiments of the invention relate to systems and methods which use a dynamic allocation of licensed transmission spectrum in conjunction with unlicensed transmission spectrum as a communication channel to meet QoS (quality of service) requirements for cost efficient, high speed and high data capacity communications.
Today, guided, or wired communications provide more capacity than unguided, or wireless radio frequency (RF) communications. As a local community networking solution for delivering high speed Internet access to schools, libraries, homes, businesses and Wi-Fi (wireless fidelity) hotspots, wireless has the distinct inherent advantage of not requiring wires and the costs associated with maintaining wires. Digital wireless has mainly been used for mobile users; however wireless is also practical for fixed position communications.
The traditional approach to using wireless spectrum is a complex procedure of assigning spectrum to various uses. This involves selling a license to a user for the exclusive use of a part of the spectrum. Once licensed, the user may use any frequencies that the license permits with restrictions on the type of transmission and levels of power.
Transceivers can communicate with other transceivers and pass digital communications to other wireless modems, to local area networks, or to the Internet. Wireless modems can achieve speeds that approximate the highest speeds available by wired alternatives. These speeds result from the combination of digital compression, error-correction, collision detection, mapping and retention of occupied frequencies, and dynamic frequency allocations.
Using these communications techniques can obviate the need to assign spectrum. A wireless modem can look for a clear channel and send a packet of data, and a return packet can be received. Some companies have been using a small and crowded portion of unlicensed spectrum, 902 to 928 MHz, for digital wireless communications.
Wireless communications can suffer from interference if the same radio spectrum is used within the geographic coverage area by another system. Most high-value, reliable wireless communications services such as cellular radio, broadband fixed wireless, television broadcasting, etc., are designed to use licensed spectrum. The use of licensed spectrum is strictly regulated and thus a license-owner has exact knowledge of any other users of the spectrum and can thus plan for it.
The very nature of licensed spectrum makes it a scarce and expensive resource. Most governments also set aside spectrum for unlicensed use to foster small users with simple devices.
Unlicensed radio spectrum is thought of as unreliable. Successful applications of unlicensed spectrum are Wi-Fi, LANs (local area networks), and cordless phones. The nature of unlicensed spectrum implies that it is impossible to predict who else might be using the same spectrum, and can therefore be an interferer.
There are technology and policy trends which are creating more opportunities for unlicensed spectrum use. There are vast areas of spectrum that are underutilized or not utilized. The tightly regulated TV broadcasting bands typically end up having large portions of unused spectrum, and there already is rulemaking in the United States to allow unlicensed operation in these bands.
As one example, television requires 6 MHz of bandwidth per channel. On the spectrum map, 376 MHz is the amount of bandwidth dedicated to television channels 14 to 69 (470 to 806 MHz). In large metropolitan areas there are conservatively 10 to 15 UHF channels using this spectrum with at least 40 empty channels. This amounts to 240 MHz of spectrum that could be used. There is additional spectrum between television broadcast channels—guard bands—that currently go unused.
There are proposed standards for wireless broadband access systems designed to deliver high speed and/or high data capacity from an Internet backbone over a four to six mile cell radius to an end user. These proposed systems include point-to-point and/or point-to-multipoint systems and operate in licensed and unlicensed spectrum over the frequencies between 2 and 11 GHz. As frequency drops, the ability for signals to pass through buildings increases for non-line-of-sight (NLOS) communications.
There are only a limited number of licensed bands in any geographic area. It is desirable for service providers to use unlicensed spectrum to provide capability to deliver high speed, high capacity data services. Additionally, a service provider may not hold licenses in every geographic area that it desires to provide service. Therefore, the use of unlicensed frequency bands may allow a service provider to cover a greater area.
The Federal Communications Commission (FCC) created a wireless arena known as the Unlicensed National Information Infrastructure (U-NII). System operators are free to operate wireless equipment in three unlicensed sub-bands: 5.15 to 5.25 GHz, 5.25 to 5.35 GHz and 5.725 to 5.825 GHz. Part 15 of the FCC document specifies the conditions for operating wireless equipment in the U-NII frequency band.
Interference is less of an issue concerning transmission within licensed bands. Most licensed bands are free of harmful interferers originating from outside sources. However, interferers can be present in unlicensed bands.
One problem with the use of unlicensed bands is that it is very difficult to control RF interference from other users. The other users may be using the selected unlicensed band for uses which are different from wireless communications. The 5.25 to 5.35 GHz and 5.725 to 5.825 GHz bands are available for broadband wireless access between two points. The same bands are also available for other wireless applications.
Interference is usually based on a signal-to-noise ratio (SNR) for any given channel. When interferers are present, some communications systems adapt by switching to a lower order modulation. For example, from 64QAM (quadrature amplitude modulation) to 16QAM, or 16QAM to QPSK (quadrature phase shift keying), or QPSK to BPSK (binary phase shift keying), or in the case of OFDM (orthogonal frequency division multiplexing) channel access, the modulation order of the subcarriers changes with SNR. Lower signal modulations are more tolerant to noise and interference, but reduce data rate.
Achieving data communications using unlicensed spectrum has proven problematic in wide-area commercial wireless services. With advances in technology that help radio devices to work around interferers, it is possible to use unlicensed spectrum that reach a high level of reliability. What is desired is a system and method for combining licensed and unlicensed spectrum as the channel for data communications.